The present invention relates to a piezoelectric actuator and its manufacturing method and an ink-jet printhead, and is suitably applied to such as an ink-jet printer device.
Heretofore, in the ink-jet printer device, ink is jetted from a nozzle corresponding to a recording signal and characters and graphics based on said recording signal can be recorded on the recording medium such as paper and film.
FIG. 11 shows an example of the construction of a conventional ink-jet printhead 1 that has been used in the ink-jet printhead device. This ink-jet printhead comprises a passage plate 2 of which one surface 2A is affixed to a nozzle plate 3 and the other surface 2B is affixed to a piezoelectric actuator 4.
In this case, pressure chambers 2C comprised of multiple concave parts are arranged on one surface side 2A of the passage plate 2 along the direction shown an arrow x1 at established intervals. And ink can be continuously supplied from the ink cartridge (not shown in Fig.) into these pressure chambers 2C through a common passage 2D respectively.
Moreover, at the edge of each pressure chamber 2C, a through path 2E is formed cutting through the passage plate 2 in the direction of its thickness (in the direction of an arrow z1), and nozzles 3A formed of multiple through holes are formed cutting through the nozzle plate 3 corresponding respectively to each through path 2E along the direction of an arrow x1 at established intervals.
On the other hand, as shown in FIGS. 11 and 12, a piezoelectric actuator 4 is comprised of multiple piezoelectric elements 6 arranged on one surface of the vibration plate 5 formed of flexible materials along the direction of an arrow x1 facing respectively to pressure chamber 2C of the passage plate 2 via said vibration plate 5, and it is fixed to said passage plate 2 affixing the other surface of the vibration plate 5 onto the other surface 2B of the passage plate 2.
At this point, each piezoelectric element 6 is polarized in the direction of its thickness (in the direction of an arrow z1). And as shown in FIG. 9, upper electrode 7A and lower electrode 7B are formed on one surface and the other surface of the piezoelectric element 6 respectively. And thus, by causing voltage difference between the upper electorde 7A and the lower electrode 7B, the piezoelectric element 6 can be deflected in the direction to displace the vibration plate 5 toward inside of the corresponding pressure chamber 2C according to the piezoelectric effects (the direction opposite to the arrow z1).
Thus, in this type of ink-jet printhead 1, by generating the voltage difference between the upper electrode 7A and the lower electrode 7B of the piezoelectric element 6 and displacing the vibration plate 5 toward inside of the corresponding pressure chamber 2C, the pressure corresponding to that deviation can be generated in the pressure chamber 2C and ink in said pressure chamber 2C can be jetted outside from the nozzle 3A under this pressure via the through path 2E.
In the ink-jet printhead 1, as disclosed in Japan Patent Laid-open No. H6-320739 bulletin, for example, the piezoelectric actuator 4 was manufactured by bonding each piezoelectric element 6 onto the vibration plate 5 using adhesives after the vibration plate 5 and piezoelectric element 6 were formed independently.
However, according to the conventional manufacturing method, it was difficult to paste multiple fine piezoelectric elements 6 precisely onto the fixed positions of the vibraion plate 5. In this connection, if the position on which the piezoelectric element 6 is to be pasted is displaced from the fixed position, the pressure based on deflection of piezoelectric element 6 cannot be generated in the corresponding pressure chamber 2C and accordingly the printing becomes unstable.
Furthermore, generally the larger the size of electric field to be printed becomes, the more the piezoelectric element warps. Therefore, in order that the conventional ink-jet printhead 1 can be driven with low voltage, each piezoelectric element 6 should be formed as thin as possible making the distance between upper electrode 7A and the lower electrode 7B short and at the same time, the viration plate 5 is formed as thin as possible and in practice, the conventional vibration plate 5 and each piezoelectric element 6 have the thickness of less than 30 (xcexcm) respectively.
However, in order to shorten the natural vibration cycle and increase the corresponding speed, the vibration plate 5 is made up of such as glass and ceramic materials having high Young""s modulus as its material. But it is difficult to make a thin sheet having less than 30 (xcexcm) using glass or ceramic materials. And heretofore, the vibration plate 5 has been made by grinding the glass plate or ceramic plate having the thickness of several hundreds (xcexcm) till it becomes thinner than 30 (xcexcm).
Accordingly, in the conventional ink-jet printhead 1, it caused problems due to the costly and time consuming manufacturing process of the vibration plate 5 and poor productivity. Moreover, the piezoelectric element 6 having thinner than 30 (xcexcm) was obtained by grinding it in the same manner as the vibration plate 5 and the realization of a piezoelectric actuator 4 having higher productivity has been desired.
Moreover, in the conventional ink-jet printhead 1, since the vibration plate 5 and each piezoelectric element 6 are formed extremely thin, these vibration plate 5 and piezoelectric element 6 are easily damaged. And in addition to the poor productivity as described above, it has caused the problem in handling at the time when manufacturing the vibration plate 5 and each piezoelectric element 6.
The present invention has been done considering the above points and is proposing a piezoelectric actuator and its manufacturing method and an ink-jet printhead capable of improving the productivity remarkably.
To obviate such problems according to the present invention, we provide a vibration layer to be arranged on one surface of the pressure chamber forming unit to cover each pressure chamber, a lower electrode layer formed of conduction materials laminated on the vibration layer, a piezoelectric layer formed of piezoelectric materials laminated on the lower electrode layer and having the size to cover multiple pressure chambers and polarized in the direction of its thickness, and an upper electrode layer formed of conduction materials laminated on the piezoelectric layer in the piezoelectric actuator, and at least either the upper electrode layer or the lower electrode layer is formed of multiple electrodes separated and formed corresponding to each pressure chamber of the pressure chamber forming unit.
As a result, since in this piezoelectric actuator, of piezoelectric layers only the part directly below each electrode of the upper electrode layer and/or the part directly above each electrode of the upper electrode layer will warp corresponding to the placement of voltage, these parts of upper electrode layer and pressure layer and the corresponding parts of the lower electrode layer and vibration layer function as an independent actuator respectively.
Accordingly, in this piezoelectric actuator it is not necessary to form the actuator by affixing fine piezoelectric materials onto the vibration layer corresponding to each pressure chamber of the pressure chamber forming unit and thus, its productivity can be remarkably improved.
Moreover, according to the present invention, we provide in the piezoelectric actuator manufacturing method, the first process for forming a pliant first sheet made up of piezoelectric materials and a pliant second sheet made up of predetermined material and as well as forming the upper electrode layer formed of conduction materials on one surface of the first sheet, forming the lower electrode layer made up of conduction materials on the other surface of the first sheet or on one surface of the second sheet, the second process for piling up and densifying the first and the second sheets having the lower electroce layer between, the third process for polarizing the first sheet in the direction of its thickness, and the fourth process for patterning the upper electrode layer to form multiple electrodes corresponding respectively to each pressure chamber of the pressure chamber forming unit.
As a result, in the piezoelectric actuator manufactured according to this piezoelectric actuator manufacturing method, since of the first piezoelectric layer formed of the first sheet, since only the part directly below each electrode of the upper electrode layer and/or the part directly above each electrode of the upper electrode layer warp responding to the voltage placement, these parts of the upper electrode layer and the pressure layer and the corresponding parts of the lower electrode layer and the vibration layer formed of the second sheet function respectively as an independent actuator.
Thus, according to this piezoelectroc actuator manufacturing method it is not necessary to form an actuator by pasting the fine piezoelectric element onto the vibration layer corresponding respectively to each pressure chamber of the pressure chamber forming unit, and thereby the productivity of the piezoelectric actuator can be outstandingly improved.
Furthermore, according to the present invention, in the piezoelectric actuator manufacturing method, the first process for forming multi-layer plate in which the upper electrode layer is laminated on one surface of the piezoelectric layer and the vibration layer is laminated on the other surface of the piezoelectric layer having the lower electrode layer between, and the second process for laminating and forming a reinforcement layer having openings with the prescribed size and shape on one surface side or the other surface side of the multi-layer together with the multi-layer plate are provided.
As a result, according to this piezoelectric actuator manufacturing method, since the multi-layer plate can be handled under the condition in which the multi-layer plate is reinforced by the reinforcement layer, breakage of said multi-layer plate can be prevented even when the multi-layer plate is very thin and the yield can be increased and thereby the productivity of the piezoelectric actuator can be remarkably improved.
Furthermore, according to the present invention, in the ink-jet printhead, the piezoelectric actuator is comprised of vibration layer to be placed to cover each pressure chamber on one surface of the pressure chamber forming unit, the lower electrode layer formed of conduction materials laminated on the vibration layer, the piezoelectric layer formed of piezoelectric materials having the size to cover multiple pressure chambers and laminated on the lower electrode layer and polarized in the direction of its thickness, and the upper electrode layer formed of conduction materials, laminated on the piezoelectric layer. And at least either the upper electrode layer or the lower electrode layer is formed with multiple electrodes separated corresponding respectively to each pressure chamber of the pressure chamber forming unit.
As a result, in this ink-jet printhead, of piezoelectric layer of the piezoelectric actuator, since only the part directly under each electrode of the upper electrode layer and/or the part directly above each electrode of the lower electrode layer warp responding to the voltage placement, these parts of the upper electrode layer and pressure layer and corresponding parts of the lower electrode layer and the vibration layer function respectively as an independent actuator.
Accordingly, in this ink-jet printheaad, it is not necessary to form the piezoelectric actuator by affixing fine piezoelectric elements onto the vibration layer corresponding respectively to each pressure chamber of the pressure chamber forming unit, and thereby the productivity of the ink-jet printhead can be remarkably improved.